The present invention relates to improved magnetic information/data recording, storage, and retrieval media and a method for manufacturing same. More specifically, the present invention relates to magnetic media in which Barkhausen noise is substantially eliminated by provision of a magnetically soft superparamagnetic underlayer, and a method for manufacturing same. The invention has particular utility in the manufacture and use of extremely high bit density magnetic recording systems utilizing a single pole vertical (i.e., perpendicular) recording head.
Magnetic media are widely used in various applications, particularly in the computer industry, and efforts are continually made with the aim of increasing the recording density, i.e., bit density of the magnetic media. In this regard, so-called xe2x80x9cperpendicularxe2x80x9d recording media have been found to be superior to the more conventional xe2x80x9clongitudinalxe2x80x9d media in achieving very high bit densities. In perpendicular magnetic recording media, residual magnetization is formed in a direction perpendicular to the surface of the magnetic medium, typically a layer of a magnetic material on a suitable substrate. Very high linear recording densities are obtainable by utilizing a xe2x80x9csingle-polexe2x80x9d magnetic transducer or xe2x80x9cheadxe2x80x9d with such perpendicular magnetic media.
It is well-known that efficient, high bit density recording utilizing a perpendicular magnetic medium requires interposition of a magnetically xe2x80x9csoftxe2x80x9d underlayer, i.e., a magnetic layer having relatively low coercivity, such as of a NiFe alloy (Permalloy), between the non-magnetic substrate, e.g., of glass, aluminum (Al) or an Al-based alloy, and the perpendicular magnetic recording layer, e.g., of a cobalt-chromium (Coxe2x80x94Cr) alloy having perpendicular anisotropy. The magnetically soft underlayer serves to guide magnetic flux emanating from the head through the perpendicular magnetic recording layer. In addition, the magnetically soft underlayer reduces susceptibility of the medium to thermally-activated magnetization reversal by reducing the demagnetizing fields which lower the energy barrier that maintains the current state of magnetization.
A typical perpendicular recording system 10 utilizing a vertically oriented magnetic medium with a soft magnetic underlayer, and a single-pole head is illustrated in FIG. 1, wherein reference numerals 2, 3, and 4 respectively indicate the substrate, soft magnetic underlayer, and vertically oriented magnetic recording layer of perpendicular magnetic medium 1, and reference numerals 6 and 7 respectively indicate the single and auxiliary poles of single-pole magnetic transducer head 5. As shown by the arrows in the figure indicating the path of the magnetic flux xcfx86, flux xcfx86 is seen as emanating from single pole 6 of single-pole magnetic transducer head 5, entering and passing through vertically oriented magnetic recording layer 4 in the region above single pole 6, entering and travelling along soft magnetic underlayer 3 for a distance and exiting therefrom and passing through vertically oriented magnetic recording layer 4 in the region above auxiliary pole 7 of single-pole magnetic transducer head 5. The direction of movement of perpendicular magnetic medium 1 past transducer head 5 is indicated in the figure by the arrow above medium 1.
However, a significant problem and drawback associated with the utilization of soft magnetic underlayers, such as layer 3 shown in FIG. 1, is the generation of noise resulting from, inter alia, pinning and unpinning of the magnetic domain walls, termed xe2x80x9cBarkhausen noisexe2x80x9d, which noise adversely affects performance characteristics of magnetic media, particularly high bit density magnetic media.
Accordingly, there exists a need for improved, high bit density perpendicular (and longitudinal) magnetic information/data recording, storage, and retrieval media including magnetically soft underlayers but which exhibit greatly reduced, or no Barkhausen noise. In addition, there exists a need for improved, low Barkhausen noise, high bit density perpendicular and longitudinal magnetic media employing magnetically soft underlayers which are fabricated by conventional manufacturing techniques, e.g., sputtering.
The present invention addresses and solves problems attendant upon the use of magnetically soft underlayers in the manufacture of high bit density perpendicular and longitudinal magnetic media, e.g., Barkhausen noise, while maintaining all structural and mechanical aspects of high bit density recording technology. Moreover, the magnetic media of the present invention can be fabricated by means of conventional manufacturing techniques, e.g., sputtering.
An advantage of the present invention is an improved, high bit density, magnetic information/data recording, storage, and retrieval medium including a magnetically soft underlayer, which medium is substantially free of Barkhausen noise.
Another advantage of the present invention is an improved, high bit density, perpendicular-type magnetic recording medium including a magnetically soft, superparamagnetic underlayer, which medium is substantially free of Barkhausen noise and well-suited for use with a single-pole magnetic transducer head.
Yet another advantage of the present invention is an improved, high bit density longitudinal-type magnetic recording medium including a magnetically soft underlayer, which medium is substantially free of Barkhausen noise.
Additional advantages, aspects, and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to an aspect of the present invention, the foregoing and other advantages are obtained in part by a high bit density magnetic information/data recording, storage, and retrieval medium substantially free of Barkhausen noise, comprising:
a non-magnetic substrate having a surface for layer stack formation thereon; and
a stack of polycrystalline layers formed over the substrate surface, the layer stack comprising, in sequence from said substrate surface:
an underlayer;
at least one layer pair composed of:
a magnetically soft superparamagnetic underlayer over-lying
the underlayer; and
an exchange de-coupling layer overlying the magnetically soft superparamagnetic underlayer; and
a high bit density magnetic recording, storage, and retrieval layer;
wherein the grains constituting each of the polycrystalline layers of the layer stack have substantially the same width.
According to embodiments of the present invention, the medium comprises a high bit density perpendicular-type or longitudinal-type magnetic recording medium; the magnetically soft superparamagnetic underlayer is from about 4 to about 12 nm thick, e.g., about 5 to about 8 nm thick, the exchange de-coupling layer is from about 0.5 to about 5 nm thick, e.g., about 0.5 to about 3 nm thick; and the width of the grains constituting each of the polycrystalline layers of the layer stack is from about 5 to about 15 nm, e.g., 10 nm.
According to further embodiments of the present invention, the magnetic medium comprises a stacked plurality of the layer pairs, each pair consisting of a magnetically soft superparamagnetic underlayer and an overlying exchange de-coupling layer.
According to yet further embodiments of the present invention, the at least one magnetically soft superparamagnetic underlayer comprises at least one ferromagnetic or ferrimagnetic material; the ferromagnetic or ferrimagnetic material being selected from iron (Fe); Fe-rich alloys, e.g., iron-chromium (Fexe2x80x94Cr) alloys; Fe-oxides; cobalt (Co); Co-rich alloys, e.g., cobalt-chromium (Coxe2x80x94Cr) alloys; and Co-oxides; and the ferromagnetic or ferrimagnetic material may include boron (B).
According to embodiments of the present invention, the exchange de-coupling layer may comprise chromium (Cr) or a Cr-based alloy; the underlayer may comprise Cr or a Cr-based alloy; and the high bit density magnetic layer comprises a Co-based alloy including one or more elements selected from Cr, Fe, Ta, Ni, Mo, Pt, V, Nb, Ge, and B.
According to further embodiments of the present invention, the non-magnetic substrate comprises glass or aluminum (Al) or an Al-based alloy, e.g., an aluminum-magnesium (Alxe2x80x94Mg) alloy, having a plating layer, e.g., of nickel-phosphorus (Nixe2x80x94P), on the surface thereof; and the medium further includes a protective overcoat layer overlying the magnetic layer and a lubricant topcoat layer overlying the protective overcoat layer.
According to another aspect of the present invention, a high bit density magnetic information/data recording, storage, and retrieval medium comprises:
a high bit density magnetic layer; and
layer means for substantially eliminating Barkhausen noise from the medium.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not limitative.